This invention relates to beam splitters and more particularly relates to splitting a beam from a fiber optic source to fiber optic receivers. The invention more particularly relates to such beam splitters having input beams that originate as the output from a source fiber optic where the split beams are suitable for being directed to a plurality of secondary fiber optics through fiber optic couplers and the use of beams from the secondary fiber optics for therapeutic treatment, such as photodynamic therapy where an undesirable area on a patient, e.g. a tumor, is exposed to a beam from a secondary fiber optic after absorption by the tumor of a photosensitizing agent such as a porphyrin derivative. More particularly photodynamic therapy is based upon accumulation in tumors of a photosensitizing drug that is activated by visible light to produce a locally cytotoxic agent. For example PHOTOFRIN(copyright), a porphyrin derivative approved for clinical use in the United States, Canada, Europe, and Japan, is activated by 630 nm light. Typically, light emitted from a tunable laser is delivered to a lesion by an optical fiber.
A problem associated with photodynamic medical procedures, e.g. photodynamic therapy, is that often numerous areas on the same patient in fact require treatment. Time involved in setting up and individually treating each of the numerous areas by a single light beam source can be extensive often exceeding the useful life of injected photosensitizing compound. Further, sequential treatment results in high cost due to time involved for trained personnel and inefficient use of costly equipment as well as significant discomfort on the part of the patient. It is of course possible to provide multiple light beam, e.g. laser, generators so that multiple areas can be simultaneously treated. Unfortunately, however, the cost for providing multiple beam generators for a single patient treatment is prohibitive.
It is known that laser beams can be split by beam splitters that comprise a partially reflective and partially transparent surface so that an incident laser beam is partially reflected and partially transmitted so that the beam is effectively split into two parts. Unfortunately, there has been no way to practically, consistently or economically commercially manufacture such surfaces so that they all will reflect 50 percent of the beam energy and transmit 50 percent of the beam energy at the same particular incident angle (the angle of the beam to the surface that splits the beam energy in half).
The manufacture of a beam splitter apparatus for more than two output beams thus would have been very difficult since the manufacturing process would have to take the particular incident angle of each individual beam splitter into consideration which requires the calculation of numerous angles of reflection and resulting various alignments and does not permit the use of any kind of standardized set angle hardware within the apparatus. The assembly of such a multiple beam splitter thus would have been tedious, time consuming and unacceptably expensive.
It has thus not been possible to easily and inexpensively manufacture a beam splitter to form four or more output beams where the output beam energies are within ten percent of each other and certainly not within five percent or less of each other.
It has been recently found that a beam splitter for a laser beam source could be made that overcame the above problems, e.g. as described in U.S. Pat. No. 6,084,717; however, such a device was not suitable for splitting a beam from a fiber optic source. Laser beam sources, e.g. as used in the device described in U.S. Pat. No. 6,084,717, are polarized, of small diameter, e.g. less than a few a millimeters, and without significant divergence. Laser beams are however expensive to produce and difficult to direct in that the entire laser source must be moved. By contrast, an input beam from a fiber optic is unpolarized, usually larger in diameter than a laser beam and has much greater divergence. A fiber optic source has definite advantages in that the beam can be easily directed simply by moving the end of the fiber optic without moving the entire light producing apparatus. Unfortunately, since beams from a fiber optic source are unpolarized, polarization thus cannot be used to attenuate individual beams from a fiber optic source. Further, even if fiber optic beam sources were conceived to be possible for use in splitters, due to divergence of beams from fiber optics, lens arrangements for laser beam sources would be completely unsuitable for beams from fiber optic sources. For example, diameter, focal length, and spacing for lenses suitable for laser beams would be different than such parameters for beams from fiber optics. Known devices for splitting beams from a laser source are thus completely unsuitable for splitting light beams from a fiber optic source.
The beam from a multimode fiber optic source is non-polarized and highly divergent.